Answering in reverse order-
Stat and tactic based. I just had an idea that some units might have a special ability for the player to redeploy them after the initial placement, in response to the enemy's deployment. But other than that, units will have to hoof it everywhere, barring some kind of transport or a special teleport rule.
The basic leadership "package" would be a higher die roll that only effects his own unit. Basically, increasing the die-size would be cheaper than increasing the base state, because of the variability versus guarantee. Like the teleport thing, I have a whole slew of unit and model "special rules" in mind, that could do thinks like letting other units use a model's Logic. I'm saving that kind of crunchy stuff for later, after I have the fundamental system hammered down.
There will be hard guidelines on stat designs. For instance, Size, Strength, and Toughness are all closely related - it's hard to imagine a creature twice the size of a man not being significantly stronger and tougher. Larger Sizes would demand a minimum in some stats, and probably cap a maximum on Agility. Likewise, Strength and Toughness being functions of mass, they couldn't be too far apart from each other, probably required to differ by no more than 50% going either way.
I don't have anything more detailed to say on model creation, especially with the weapon and armor system still up in the air. But feel free to brainstorm all the unit designs you like. Heck, I encourage you post them. The more ideas I get for things to make, the better I'll know how to shape the system.